Allow args for editor via env variable

[gutsytechster]

This works for the Python3 only as the implementation uses methods
which are only supported by the Python3.

This fixes #7392

[gutsytechster]

I still have to write tests. However, I am unsure about the location where tests should go? Also, should the helper function go into utils/misc or is it fine here?

[deveshks]

Suggested change

	# Currently mypy fails for Python2 as it could not recognise the
	# shutil.which()
	# mypy fails for Python2 as shutil.which() is not supported

[pradyunsg]

I still have to write tests

I think you can put them in tests/unit/test_configuration.py.

Also, should the helper function go into utils/misc or is it fine here?

Staying in this module is fine, but since it doesn't use self, I'd suggest making it a module-level function instead of a method.

[pradyunsg]

I suggest moving all the not-subprocess-call stuff into _determine_editor and then, changing the original subprocess call line to:

subprocess.check_call(editor_args + [fname])

[pradyunsg]

Thanks for picking this up @gutsytechster! ^.^

(1) I suggest moving all the not-subprocess-call stuff to just-after _determine_editor (and out of the try-except) and then, changing the original subprocess call line to:

subprocess.check_call(editor_command + [fname])

(2) The check for PY3 can probably be moved into _get_editor_cmd (which I suggest renaming to parse_editor_value()) so that we have a direct assignment here, which would be cleaner IMO.

if PY2:
    return [editor]
...

This might also help with the mypy situation, since mypy will recognize (AFAIK) the if PY2: on Python 2. If not, just say Python 2 (not Python2) so that it can show up as part of a Python 2|PY2 search that we'll be doing later in the year. :)

[pradyunsg]

Going to go ahead and close this, since the underlying issue has been resolved. Thanks @gutsytechster for filing this PR! ^>^